Evidence has been obtained that an estrogen=induced chick oviduct membrane glycoprotein is the transferrin receptor. Estrogen treatment elicits oviduct differentiation which includes the biosynthesis of egg white proteins. One of the egg white proteins, conalbumin (ovotransferrin), serves as an iron source for the developing embryo. In order to obtain the large amounts of iron necessary for conalbumin secretion the oviduct transferrin receptor is also estrogen-induced. Antibodies and/or a specific oligonucleotide probe (based on N-terminal sequence analysis) will be employed to obtain a transferrin receptor cDNA from a lambda gtll expression library. The cDNA will be used to obtain protein sequence and to measure steady-state mRNA levels, transcriptional activity of receptor mRNA and mRNA half-life. The segregation of transferrin receptor from conalbumin (ovotransferrin) during movement from their-site(s) of synthesis to the cell surface will be studied using transferrin receptor antibodies, conalbumin antibodies and immunoelectron microscopy with gold- or ferritin- conjugated secondary antibodies. Additionally, an attempt will be made to obtain the putative transferrin receptor-specific vesicles by sucrose gradient centrifugation. Depending on the outcome of the segregation studies additional experiments may be undertaken to determine when the transferrin receptor acquires its binding capability and how that might affect vesicular segregation.